1. Field of the Invention
This invention relates to a system for detecting on a real time basis the variations in frequency spectrum of the output signals from various detectors disposed at several locations in a nuclear power plant, especially the frequency values, the locations at which anomalous peaks occur on the power spectral densities (hereinafter referred to as PSDs) of the detector output signals.
2. Description of the Prior Art
Frequency spectrum analyzers have hitherto been used to monitor the variations in frequency spectrum of signals. The frequency spectrum analyzer, however, is expensive and rather voluminous. In addition, the analyzer takes relatively much time for data processing and it is difficult for the analyzer to monitor many signals on a real time basis. The Japanese Patent Application Laid-Open No. 87941/76 discloses a system in which the variation in frequency spectrum of a signal is detected by monitoring continuously the average frequency and the RMS value given by the following equation (1): ##EQU1## Here, .nu.(t) is the average frequency at time instant t, .omega. the angular frequency, S(.omega., t) the short-time PSD, .sigma.(t) the RMS value of the signal at time instant t, and .mu.(t) the RMS value of the time-derivative of the signal. When the signal has a relatively broad frequency range, the average frequency given by the equation (1) will have a small variation even though an anomalous peak occurs on the frequency spectrum. Accordingly, it is difficult in the above-described prior art system to detect the geometrical variation in the frequency spectrum and to estimate the frequency value at which the anomalous peak occured.